Two-stage electromagnetic induction transformer

ABSTRACT

A transformer has a first winding, a second winding, a third winding, a fourth winding and a fifth winding. The fifth winding has a first part and a second part serially connected to the first part. The first part is magnetically coupled to the second winding and magnetically isolated from the first winding, and the second part is magnetically coupled to the fourth winding and magnetically isolated from the third winding. The second winding is positioned between the first winding and the first part, the first winding is positioned adjacent to the second winding, and the second winding is positioned adjacent to the first part. The fourth winding is positioned between the third winding and the second part, the third winding is positioned adjacent to the fourth winding, and the fourth winding is positioned adjacent to the second part.

CROSS REFERENCE TO RELATED APPLICATION

This patent application is a divisional application of and claimspriority to U.S. patent application Ser. No. 14/886,109, filed on Oct.19, 2015, and entitled “TWO-STAGE ELECTROMAGNETIC INDUCTIONTRANSFORMER”. Patent application Ser. No. 14/886,109 claims the benefitof Taiwan Patent Application No. 103136202 filed on Oct. 20, 2014 andTaiwan Patent Application No. 104114108 filed on May 4, 2015. The entirecontents of which are incorporated herein by reference.

TECHNICAL FIELD

The technical field relates to a transformer, and more particularly, toa two-stage electromagnetic induction transformer.

BACKGROUND

Transformers have been popularly used in many electric or powerapparatuses to pull up/down voltages or provide impedance matching.Basically, the impedance matching would be adjusted according toequipment requirement (e.g. gain, efficiency, power, signal-to-noiseratio (SNR), etc.). For instance, in order to optimize the powerdelivered from a signal source to a load circuit, an impedance ratio ofthe transformer may be adjusted, such that the output impedance of thesignal source would match the impedance of the load circuit.

In the field of impedance matching, a lot of techniques have beendisclosed. For example, Macphail disclosed “Switched impedancetransformer for semiconductor circuits” in U.S. Pat. No. 7,616,934. Leeet al. disclosed “Systems and methods for a SPDT switch or SPMT switchwith transformer” in U.S. Pat. No. 8,044,540.

SUMMARY

An embodiment of the present invention provides a transformer. Thetransformer comprises a first winding, a second winding and a thirdwinding. The first winding is configured to receive a first input signalto generate a first signal. The second winding is magnetically coupledto the first winding and configured to generate a second signal throughelectromagnetic induction with the first winding or by receiving asecond input signal. The third winding is magnetically coupled to thesecond winding, magnetically isolated from the first winding, andconfigured to electromagnetically induct with the second winding andoutput an output signal. The second winding is positioned between thefirst winding and the third winding, the first winding is positionedadjacent to the second winding, and the second winding is positionedadjacent to the third winding.

Another embodiment of the present invention provides a transformer. Thetransformer comprises a first winding, a second winding, a thirdwinding, a fourth winding and a fifth winding. The fifth winding has afirst part and a second part serially connected to the first part. Thefirst part is magnetically coupled to the second winding andmagnetically isolated from the first winding, and the second part ismagnetically coupled to the fourth winding and magnetically isolatedfrom the third winding. The second winding is posited between the firstwinding and the first part, the first winding is posited adjacent to thesecond winding, and the second winding is posited adjacent to the firstpart. The fourth winding is posited between the third winding and thesecond part, the third winding is posited adjacent to the fourthwinding, and the fourth winding is posited adjacent to the second part.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a circuit diagram of radio frequency amplifier according to anembodiment of the present invention.

FIG. 2 is a layout diagram of a transformer according to an embodimentof the present invention.

FIG. 3 is a layout diagram of a winding W1, a winding W2 and a firstpart L1 shown in FIG. 2.

FIG. 4 is an enlarged view of the windings W1 and W2 and the first partL1 of the transformer located within an area shown in FIG. 3.

FIG. 5 is a layout diagram of the winding W1, the winding W2 and thefirst part L1 of another transformer according to another embodiment ofthe present invention.

FIG. 6 is an exploded diagram of the winding W1, the winding W2 and thefirst part L1 of a transformer according to another embodiment of thepresent invention.

FIG. 7 is a schematic diagram of conductors M1 and M2 and a winding W2of the transformer shown in FIG. 6.

FIG. 8 is an exploded diagram of the winding W1, the winding W2 and thefirst part L1 of a transformer according to another embodiment of thepresent invention.

FIG. 9 is a schematic diagram of conductor M1 and M2 of a winding W2 ofthe transformer shown in FIG. 8.

FIG. 10 is a circuit diagram of radio frequency amplifier according toanother embodiment of the present invention.

FIG. 11 is a layout diagram of a transformer according to anotherembodiment of the present invention.

FIG. 12 is an enlarged view of the windings W1, W2 and W3 of thetransformer located within an area shown in FIG. 11.

DETAILED DESCRIPTION

Below, exemplary embodiments will be described in detail with referenceto accompanying drawings so as to be easily realized by a person havingordinary knowledge in the art. The inventive concept may be embodied invarious forms without being limited to the exemplary embodiments setforth herein. Descriptions of well-known parts are omitted for clarity,and like reference numerals refer to like elements throughout.

Please refer to FIG. 1. FIG. 1 is a circuit diagram of radio frequency(RF) amplifier 100 according to an embodiment of the present invention.The RF amplifier 100 is coupled to a load circuit 200 and comprises fouramplifiers 110-140 and a transformer 10. The transformer 10 compriseswindings W1 to W5. The winding W5 comprise a first part L1 and a secondpart L2. The first part L1 and the second part L2 are connected inserial. The winding W1 is configured to receive an input signal IN1 andgenerate a signal S1. The winding W2 is magnetically coupled to thewinding W1 and is configured to generate a signal S2 throughelectromagnetic induction with the winding W1 and/or by receiving aninput signal IN2. The winding W3 is configured to receive an inputsignal IN3 and generate a signal S3. The winding W4 is magneticallycoupled to the winding W3 and is configured to generate a signal S4through electromagnetic induction with the winding W3 and/or byreceiving an input signal IN4. The first part L1 is magnetically coupledto the winding W2 and magnetically isolated from the winding W1, and thesecond part L2 is magnetically coupled to the winding W4 andmagnetically isolated from the winding W3. The first part L1 and thesecond part L2 of the fifth winding W5 are configured to generate asignal S5 respectively through electromagnetic induction with thewinding W2 and the winding W4, and to output an output signal S_(OUT)from an end P11 of the second part L2. The winding W2 is positionedbetween the winding W1 and the first part L1, and the winding W4 ispositioned between the winding W3 and the second part L2. The winding W1is positioned adjacent to the winding W2, the winding W2 is positionedadjacent to the first part L1, the winding W3 is positioned adjacent tothe winding W4, and the winding W4 is positioned adjacent to the partsecond L2. In the below description, it would explain how toelectromagnetically isolate the first part L1 from the winding W1 andhow to electromagnetically isolate the second part L1 from the windingW3. Moreover, when the input signal IN1 is inputted to the winding W1,the winding W1 generates the signal S1. The signal S2 generated by thewinding W2 may be resulted from inputting the input signal IN2 to thewinding W2, electromagnetic induction with the first winding W1, or bothinputting the input signal IN2 to the winding W2 and the electromagneticinduction with the first winding W1. Similarly, when the input signalIN3 is inputted to the winding W3, the winding W3 generates the signalS3. The signal S4 generated by the winding W4 may be resulted frominputting the input signal IN4 to the winding W4, electromagneticinduction with the first winding W3, or both inputting the input signalIN4 to the winding W4 and the electromagnetic induction with the firstwinding W3.

The amplifiers 110, 120, 130 and/or 140 may be high-frequency amplifiersor power amplifiers in view of their functions. In view of the numbersof input/output ends of the amplifiers 110 to 140, the amplifiers 110,120, 130 and/or 140 may be single-ended amplifiers or differentialamplifiers. However, the present invention is not limited thereto. Inthe embodiment, the amplifiers 110 to 140 are differential amplifiers.Input ends of the amplifiers 110, 120, 130 and 140 are coupled to asignal sources O1, O2, O3 and O4 respectively. The amplifiers 110, 120,130 and 140 respectively amplify signals outputted from the signalsources O1, O2, O3 and O4 to output the input signals IN1, IN2, IN3 andIN4 according to enable signals En1, En2, En3 and En4. Output end T1,T3, T5 and T7 of the amplifiers 110, 120, 130 and 140 are respectivelycoupled to ends P1, P3, P5 and P7 of the windings W1, W2, W3 and W4, andthe input signals IN1, IN2, IN3 and IN4 are respectively inputted to thewindings W1, W2, W3 and W4 through the ends P1, P3, P5 and P7 of thewindings W1, W2, W3 and W4. Moreover, the amplifiers 110, 120, 130 and140 respectively further comprise output ends T2, T4, T6 and T8respectively, which are coupled to the ends P2, P4, P6 and P8 of thewindings W1, W2, W3 and W4.

In the embodiment, the amplifier 110 is activated by an enable signalEn1 so as to output the input signal IN1 to the winding W1. Similarly,the amplifier 120 is activated by an enable signal En2 so as to outputthe input signal IN2 to the winding W2; the amplifier 130 is activatedby an enable signal En3 so as to output the input signal IN3 to thewinding W3; and the amplifier 140 is activated by an enable signal En4so as to output the input signal IN4 to the winding W4. It is noted thatthe power of the signal S2 generated by the winding W2 would be changedwhen the amplifier 120 is activated by an enable signal En2, and thatthe power of the signal S4 generated by the winding W4 would be changedwhen the amplifier 140 is activated by an enable signal En4. The enablesignals En1, En2, En3 and En4 may be the power supply signals of theamplifiers 110, 120, 130 and 140, control signals of a bias circuit,system voltages (VDD or VCC) of the radio frequency amplifier 110 orbias voltages of the radio frequency amplifier 110.

Moreover, the impedance matching of the radio frequency amplifier 110could be adjusted by enabling/disabling the amplifiers 110, 120, 130and/or 140. In detail, the impedance matching provided by thetransformer 10 could be switched among a first impedance matching, asecond impedance matching, a third impedance matching and a fourthimpedance matching based on the enable signals En1, En2, En3 and En4.When one of the input signals IN1 and IN3 is inputted, and the inputsignals IN2 and IN4 and another of the input signals IN1 and IN3 are notinputted, the transformer 10 provides the first impedance matching. Forexample, when the amplifier 110 is enabled and the amplifiers 120, 130and 140 are disabled, the transformer 10 provides the first impedancematching by performing a two-stage electromagnetic induction whichcomprises the electromagnetic induction between the windings W1 and W2resulted from inputting the signal IN1 and the electromagnetic inductionbetween the winding W2 and the first part L1 which results in thegeneration of the signal S5. Moreover, when the input signals IN1 andIN3 are inputted, and the input signals IN2 and IN4 are not inputted,the transformer 10 provides the second impedance matching. That is, whenthe amplifiers 110 and 130 are enabled and the amplifiers 120 and 140are disabled, the transformer 10 provides the second impedance matching.Further, when one of the input signals IN2 and IN4 is inputted, and theinput signals IN1 and IN3 and another of the input signals IN2 and IN4are not inputted, the transformer 10 provides the third impedancematching. For example, when the amplifier 120 is enabled and theamplifiers 110, 130 and 140 are disabled, the transformer 10 providesthe third impedance matching by performing electromagnetic inductionbetween the winding W2 and the first part L1 to generate which resultsin the generation of the signal S5. In addition, when the input signalsIN2 and IN4 are inputted, and the input signals IN1 and IN3 are notinputted, the transformer 10 provides the fourth impedance matching.That is, when the amplifiers 120 and 140 are enabled and the amplifiers110 and 130 are disabled, the transformer 10 provides the fourthimpedance matching. Furthermore, the transformer 10 may provide a fifthimpedance matching by enabling the amplifiers 110, 120, 130 and 140.Accordingly, the impedance matching provided by the transformer 10 couldbe switched among the first impedance matching, the second impedancematching, the third impedance matching, the fourth impedance matchingand the fifth impedance matching.

In an embodiment the transformer ratios of the windings W1, W2 and thefirst part L1 is 4:2:1, the transformer ratios of the windings W3-W4 andthe second part L2 is 4:2:1, the inductances of the windings W1 and W3are the same, the inductances of the windings W2 and W4 are the same,the inductances of the first part L1 and the second part L2 are thesame, and the load impedance of the load circuit 200 is 50Ω. Therefore,the first impedance matching is equal to 50×4=200Ω, the second impedancematching is equal to 50/4=12.5Ω, the third impedance matching is equalto 50×2=100Ω, the fourth impedance matching is equal to 50/2×2=50Ω, anda typical value (i.e., an equivalent value which is regarded that thesecond impedance matching and the fourth impedance matching areconnected in parallel) of fifth impedance matching is equal to

$\frac{\left( {100 \times 50} \right)}{\left( {100 + 50} \right)} = {33.3\mspace{11mu}{\Omega.}}$Thus, the typical value of the fifth impedance matching is less than orequal to the fourth impedance matching, the fourth impedance matching isless than or equal to the third impedance matching, the third impedancematching is less than or equal to the second impedance matching, and thesecond impedance matching is less than or equal to the first impedancematching.

Moreover, the operation of inputting the input signal IN1 to the windingW1 is performed according to the enable signal En1, the operation ofinputting the input signal IN2 to the winding W2 is performed accordingto the enable signal En2, the operation of inputting the input signalIN3 to the winding W3 is performed according to the enable signal En3,and the operation of inputting the input signal IN4 to the winding W4 isperformed according to the enable signal En4. Therefore, the transformer10 may provide the first impedance matching by inputting the inputsignal IN1 to the winding W1, such that the load impedance of the outputsignal S_(OUT) matches the input signal IN1. Moreover, the transformer10 may provide the second impedance matching by inputting the inputsignals IN1 and IN2 to the windings W1 and W3, such that the loadimpedance of the output signal S_(OUT) matches the input signals IN1 andIN3. In addition, the transformer 10 may provide the third impedancematching by inputting the input signal IN2 to the winding W2, such thatthe load impedance of the output signal S_(OUT) matches the input signalIN2. Further, the transformer 10 may provide the fourth impedancematching by inputting the input signals IN2 and IN4 to the windings W2and W4, such that the load impedance of the output signal S_(OUT)matches the input signals IN2 and IN4. Therefore, by inputting the inputsignals IN1, IN2, IN3 and/or IN4, the impedance matching provided by thetransformer 10 would be switched among the first impedance matching, thesecond impedance matching, the third impedance matching and the fourthimpedance matching. Wherein, the transformer 10 provides the firstimpedance matching when the input signal IN1 is inputted and the inputsignals IN2, IN3 and IN4 are not inputted. The transformer 10 providesthe second impedance matching when the input signals IN1 and IN3 areinputted and the input signals IN2 and IN4 are not inputted. Thetransformer 10 provides the third impedance matching when the inputsignal IN2 is inputted and the input signals IN1, IN3 and IN4 are notinputted. The transformer 10 provides the fourth impedance matching whenthe input signals IN2 and IN4 are inputted and the input signals IN1 andIN3 are not inputted. Moreover, when the input signals IN1, In2, IN3 andIN4 are respectively inputted to the windings W1, W2, W3 and W4 of thetransformer 10, the transformer 10 provides the fifth impedancematching.

Moreover, the output power of the RF amplifier 100 could be adjustedaccording to the enable signals En1, En2, En3 and En4. In an embodimentof the present invention, it is supposed that the output power of the RFamplifier 100 is equal to PW1 when the amplifier 110 is enabled and theamplifiers 120, 130 and 140 are disabled, that the output power of theRF amplifier 100 is equal to PW2 when the amplifiers 110 and 130 areenabled and the amplifiers 120 and 140 are disabled, that the outputpower of the RF amplifier 100 is equal to PW3 when the amplifier 120 isenabled and the amplifiers 110, 130 and 140 are disabled, and that theoutput power of the RF amplifier 100 is equal to PW4 when the amplifiers120 and 140 are enabled and the amplifiers 110 and 130 are disabled. Inthe embodiment, the output power of the amplifier 120 is greater thanthat of the amplifier 110, and the output power of the amplifier 140 isgreater than that of the amplifier 130, then PW4>PW3>PW2>PW1 and theoutput power of the RF amplifier 100 is substantially equal to (PW2+PW4)when all of the amplifiers 110, 120, 130 and 140 are enabled and theenergy losses are ignored. Therefore, the output power of the RFamplifier 100 could be switched to 0, PW1, PW2, PW3, PW4 or (PW2+PW4)according to the enable signals En1, En2, En3 and En4. Accordingly,various demands for the output power of the RF amplifier 100 would besatisfied.

In an embodiment of the present invention, it is supposed that thewinding W1 has an equivalent inductance I1, the winding W2 has anequivalent inductance I2 and the first part L1 has an equivalentinductance I5. The equivalent inductances I1, I2 and I5 are sequentiallyincreasing or decreasing, and such relationships among the equivalentinductances I1, I2 and I5 may be determined according to the practicaldemands of the application of the circuit (e.g. gain, efficiency, power,SNR, etc.). In other words, relationships among the equivalentinductances I1, I2 and I5 may be I1>I2>I5 or I1<I2<I5. The equivalentinductances I1, I2 and I5 would be determined by adjusting the turns orwidths of the windings W1, W2 and the first part L1. Take adjusting theturns of the windings W1, W2 and the first part L1 for example, ifI1>I2>I5, a number of turns of the winding W1 is greater than a numberof turns of the winding W2, and the number of turns of the winding W2 isgreater than a number of turns of the first part L1. Take adjusting thewidths of the windings W1, W2 and the first part L1 for example, ifI1>I2>I5, the width of the winding W1 is less than the width of thewinding W2, and the width of the winding W2 is less than the width ofthe first part L1. Similarly, it is supposed that the winding W3 has anequivalent inductance I3, the winding W4 has an equivalent inductance I5and the second part L2 has an equivalent inductance I6. The equivalentinductances I3, I4 and I6 may be sequentially increasing or decreasing.In other words, relationships among the equivalent inductances I3, I4and I6 may be I3>I4>I6 or I3<I4<I6. The equivalent inductances I3, I4and I6 would be determined by adjusting the turns or widths of thewindings W3-W4 and the first part L2.

In an embodiment of the present invention, I1<I2<I5, I3<I4<I6, theoutput power of the amplifier 120 is less than the output power of theamplifier 110, and the output power of the amplifier 140 is less thanthe output power of the amplifier 130. For example, if the ratios ofI1:I2:I5 are 1:2:4 and the ratios of I3:I4:I6 are 1:2:4, then thetransformer ratios of the windings W1, W2 and first part L1 would be1:2:4 and the transformer ratios of the windings W3, W4 and second partL2 would be also 1:2:4. If the load impedance of the load circuit 200 is400Ω, the first impedance matching is equal to 400/4=100Ω, the secondimpedance matching is equal to 400/2×¼=50Ω, the third impedance matchingis equal to 400× 2/4=200Ω, and the fourth impedance matching is equal to400× 2/4=100Ω. Thus, the second impedance matching is less than or equalto the first impedance matching, the first impedance matching is lessthan or equal to the fourth impedance matching, and the fourth impedancematching is less than or equal to the third impedance matching. Inanother embodiment of the present invention, the output power of theamplifier 120 is greater than the output power of the amplifier 110, andthe output power of the amplifier 140 is greater than the output powerof the amplifier 130, such that I1>I2>I5 and I3>I4>I6.

Since the transformer 10 outputs the signal S5 by performing thetwo-stage electromagnetic induction by the windings W1, W2, W3, W4 andW5, as compared to a prior art transformer which performs single-stageelectromagnetic induction, the transformer 10 of an embodiment of thepresent invention has a smaller constant quality factor circle (constantQ circle), the transformer 10 and the RF amplifier 100 have a greaterbandwidth and a less insertion loss. Moreover, the transformer 10 wouldhave a smaller compact area in a condition that the transformer ratiosare the same.

In an embodiment of the present invention, the RF amplifier 100 is usedas a transmitter in a radio frequency (RF) device, and the input signalsIN1, IN2, IN3, IN4 and IN4 may be different RF signals. According to theenable signals En1, En2, En3 and En4, the output power of thetransmitter of the RF device could be switched among various outputpowers and the impedance matching of the RF amplifier 100 could beadjusted simultaneously.

Moreover, if the amplifiers 120 and 140 are differential amplifiers, acapacitor C1 may be added and coupled between two output ends T3 and T4of the amplifier 120, and a capacitor C2 may be added and coupledbetween two output ends T7 and T8 of the amplifier 140. In the conditionthat the impedance matchings to which the RF amplifier 100 could beswitched are fixed, the required equivalent inductance of each windingcould be reduced by connecting the capacitor C1 with the windings W1, W2and the first part L1 in parallel and connecting the capacitor C2 withthe windings W3, W4 and the second part L2.

In a preferred embodiment of the present invention, if few flux lossresulted from routing the windings is ignored, the windings W1 and W2are substantially completely magnetically coupled, the winding W2 andthe first part L1 are substantially completely magnetically coupled, andthe first part L1 is substantially completely magnetically isolated fromthe winding W1. In an embodiment of the present invention, a distancebetween the winding W1 and the first part L1 exits and is not too great,such that the winding W1 and the first part L1 would be substantiallycompletely magnetically coupled if the winding W2 is not provided tosupply magnetic isolation between the winding W1 and the first part L1.Moreover, the plane on which the windings W1, W2 and the first part L1are positioned is parallel with a reference plane or coincides with thereference plane, and geometry centers of the three windings W1, W2 andthe first part L1 projected on the reference plane substantiallycoincide with each other. A plurality of embodiments of the presentinvention would be set forth in the below description. Please refer toFIGS. 2, 3 and 4. FIG. 2 is a layout diagram of a transformer 10according to an embodiment of the present invention. FIG. 3 is a layoutdiagram of the windings W1, W2 and the first part L1 shown in FIG. 2.FIG. 4 is an enlarged view of the windings W1, W2 and the first part L1of the transformer 10 located within an area 2101 or 2102 shown in FIG.3. In the embodiment, because layouts of the winding W1, the winding W2and the first part L1 are almost symmetrical with the layouts of thewinding W3, the winding W4 and the second part L2, the descriptions ofthe layouts of the winding W1, the winding W2 and the first part L1could be used to explain the layouts of the winding W3, the winding W4and the second part L2.

In the embodiment of FIGS. 2-4, the reference plane is XY plane formedby X axis and Y axis, and a section B1 of the winding W1, a plurality ofsections B2 of the winding W2 and a plurality of sections B5 of thefirst part L1 are positioned within each area 2101 or 2102 on XY plane.The section B1, the sections B2 and the sections B5 are parallel withinthe area 2101 or 2102. Moreover, the sections B2 are positioned adjacentto two sides of the section B1 and adjacent inner sides of the sectionsB5. Due to the foresaid positing of the windings W1, W2 and the firstpart L1, the windings W1 and W2 are substantially completelymagnetically coupled, the winding W2 and the first part L1 aresubstantially completely magnetically coupled, and the first part L1 issubstantially completely magnetically isolated from the winding W1 bythe winding W2. Moreover, the windings W1, W2 and the first part L1 forman inner ring 240 and an outer ring 250. The inner ring 240 is formedwithin a plurality of areas 2101, and the outer ring is formed within aplurality of areas 2102. The geometry centers of the windings W1, W2 andthe first part L1 (i.e. the centers of the areas surrounded by thewindings W1, W2 and the first part L1) are a point O on the XY plane, orthe geometry centers of the windings W1, W2 and the first part L1 almostcoincide with each other. Similarly, a section B3 of the winding W3, aplurality of sections B4 of the winding W4 and a plurality of sectionsB6 of the second part L2 are positioned within each area 2101 or 2102 onXY plane, and the layouts of the sections B3, B4 and B6 are almostsymmetrical with the layouts of the sections B1, B2 and B5. Therefore,detail descriptions of the sections B3, B4 and B6 are omitted for thesake of simplification.

Moreover, the sections of the windings W1, W2 and the first part L1within the areas 2103 and 2104 are formed on different planes. Thesections B2 of the winding W2 within the areas 2103 and 2104 stretchover the sections B1 of the winding W1, and the sections B5 of the firstpart L1 within the areas 2103 and 2104 stretch over the sections B2 ofthe winding W2. The two sections B2 of the winding W2 within the area2103 are interlaced and not contact to each other so as to connect thesections B2 located at the inner ring 240 and the outer ring 250. Thetwo sections B1 of the winding W1 within the area 2104 are interlacedand not contact to each other so as to connect the sections B1 locatedat the inner ring 240 and the outer ring 250. The two sections B5 of thefirst part L1 within the area 2104 are interlaced and not contact toeach other so as to connect the sections B3 located at the inner ring240 and the outer ring 250. In an embodiment of the present invention,the sections B2 of the winding W2 within the area 2013 may completelyoverlap the entire area 2103 so as to isolate the sections B1 within thearea 2103 from the sections B5 within the area 2103. In an embodiment ofthe present invention, the windings W1, W2 and the first part L1 arerespectively formed by the sections B1, B2 and B5 within a single area2101 or 2102 as shown in FIG. 3. The geometry center of the section B1,the geometry center of the sections B2 and the geometry center of thesections B5 are a point O′ on the XY plane, or the geometry center ofthe section B1, the geometry center of the sections B2 and the geometrycenter of the sections B3 almost coincide with each other.

Please refer to FIG. 5. FIG. 5 is a layout diagram of the winding W1,the winding W2 and the first part L1 of another transformer according toanother embodiment of the present invention. As compared to FIG. 3, thepositions of the winding W1 and the first part L1 are switched in FIG.5.

Please refer to FIGS. 6 and 7. FIG. 6 is an exploded diagram of thewinding W1, the winding W2 and the first part L1 of a transformeraccording to another embodiment of the present invention. FIG. 7 is aschematic diagram of conductors M1 and M2 and the winding W2 of thetransformer shown in FIG. 6. The ends P9 and P10 of the first part L1 inFIG. 6 may be corresponded to the ends P9 and P10 of the first part L1in FIG. 1. In the embodiment, the windings W1, W2 and the first part L1are positioned on three different parallel planes. In detail, the threeparallel planes on which the W1, W2 and the first part L1 are positionedare parallel with the XY plane, and the coordinates of the threeparallel planes on the Z axis are different. Moreover, as shown in FIG.7, the conductors M1 and M2 and the winding W2 are positioned on thesame plane, the conductor M1 is positioned adjacent to an outer side ofthe winding W2 and substantially surrounds the winding W2, and theconductor M2 is positioned adjacent to an inner side of the winding W2.In an embodiment of the present invention, the conductors M1 and M2 aregrounded to provide a better magnetic isolation between the winding W1and the first part L1. Moreover, as shown in FIG. 6, the corner-pointsa1, b1, c1 and d1 of the winding W1 respectively align with thecorner-points a2, b2, c2 and d2 of the winding W2 and the corner-pointsa3, b3, c3 and d3 of the first part L1. If the plane on which thewinding W2 is positioned is regarded as the reference plane, projectedgeometry centers of the winding W1 and the first part L1 on thereference plane would be or almost coincide with the center of the areasurrounded by the winding W2 (i.e. the geometry center of the windingW2). In an embodiment of the present invention, the windings W1, W2 andthe first part L1 are electrically disconnected. In another embodimentof the present invention, the windings W1, W2 and the first part L1 aregrounded or coupled to a power supply. Moreover, the widths of thewindings W1, W2 and the first part L1 may be the same, and the two endsP1 and P2 of the winding W1, the two ends P3 and P4 of the winding W2and the two ends P5 and P6 of the first part L1 are respectivelypoisoned on three different sides of the transformer 10. Due to theforesaid positing of the windings W1, W2 and the first part L1, thewindings W1 and W2 are substantially completely magnetically coupled,the winding W2 and the first part L1 are substantially completelymagnetically coupled, and the first part L1 is substantially completelymagnetically isolated from the winding W1 by the winding W2.

Please refer FIGS. 8 and 9. FIG. 8 is an exploded diagram of the windingW1, the winding W2 and the first part L1 of a transformer according toanother embodiment of the present invention. FIG. 9 is a schematicdiagram of conductor M1 and M2 of a winding W2 of the transformer shownin FIG. 8. The difference between the transformers in FIGS. 8 and 6 isthe structure of the conductor(s) M2. As shown in FIG. 9, thetransformer 10 comprises a plurality of bar-shaped conductors M2. Theconductors M2 are separated and parallel substantially. The purpose ofpositing the conductors M2 is to avoid increasing of the quality factor(i.e. Q factor) of the transformer 10 due to the eddy current of thetransformer 10.

In summary, the embodiments of the present invention providetransformers, and each of the transformers has a first part magneticallyisolated from a first winding by a second winding. Moreover, thetransformer outputs a third signal by performing a two-stageelectromagnetic induction by the winding W1, the winding W2 and thefirst part L1. As compared to a prior art transformer which performssingle-stage electromagnetic induction, the transformer of the presentinvention has a smaller constant quality factor circle (constant Qcircle). Accordingly, as compared to the prior art transformer, thetransformer and the RF amplifier of the present invention have a greaterbandwidth and a less insertion loss. In a condition that the transformeraccording to the present invention has the same transformer ratios asthe prior, the transformer of the present invention has a smallercompact area. Moreover, the RF amplifier of the present invention wouldobtain optimum impedance matchings for different output powers.

Please refer FIG. 10. FIG. 10 is a circuit diagram of radio frequencyamplifier 1100 according to another embodiment of the present invention.The RF amplifier 1100 is coupled to a load circuit 1130 and comprisestwo amplifiers 1110 and 1120 and a transformer 1010. The transformer1010 comprises three windings W11, W12 and W13. The winding W11 isconfigured to receive an input signal IN11 and generate a signal S11.The winding W12 is magnetically coupled to the winding W11 and isconfigured to generate a signal S12 through electromagnetic inductionwith the first winding W11 and/or by receiving another input signalIN12. The winding W13 is magnetically coupled to the winding W12 andmagnetically isolated from the winding W11. The winding W13 isconfigured to generate a signal S13 and output a signal S_(OUT) throughelectromagnetic induction with the second winding W12. The winding W12is positioned between the windings W11 and W13. The winding W11 ispositioned adjacent to the winding W12, and the winding W12 ispositioned adjacent to the winding W13. In the below description, itwould explain how to electromagnetically isolate the winding W13 fromthe winding W11. Moreover, when the input signal IN11 is inputted to thewinding W11, the winding W11 generates the signal S11. The signal S12generated by the winding W12 may be resulted from inputting the inputsignal IN12 to the winding W12, electromagnetic induction with the firstwinding W11, or both inputting the input signal IN2 to the winding W12and the electromagnetic induction with the first winding W11.

The amplifiers 1110 and/or 1120 may be high-frequency amplifiers orpower amplifiers in view of their functions. In view of the numbers ofinput/output ends of the amplifiers 1110 and 1120, the amplifiers 1110and/or 1120 may be single-ended amplifiers or differential amplifiers.However, the present invention is not limited thereto. In theembodiment, the amplifiers 1110 and 1120 are differential amplifiers. Aninput end of the amplifier 1110 is coupled to a signal source O11, andan input end of the amplifier 1120 is coupled to a signal source O12.The amplifiers 1110 and 1120 respectively amplify signals outputted fromthe signal sources O11 and O12 to output the input signals IN11 and IN12according to enable signals En11 and En12. An output end T11 of theamplifier 1110 is coupled to an end P101 of the winding W11, and theinput signal IN11 is output from the amplifier 1110 to the end P101 ofthe winding W11. An output end T13 of the amplifier 1120 is coupled toan end P103 of the winding W12, and the input signal IN12 is output fromthe amplifier 1120 to the end P103 of the winding W12. Moreover, theamplifiers 1110 and 1120 further comprise output ends T12 and T14respectively, which are coupled to the ends P102 and P104 of thewindings W11 and W12.

In the embodiment, the amplifier 1110 is activated by an enable signalEn11 so as to output the input signal IN11 to the winding W11.Similarly, the amplifier 1120 is activated by an enable signal En12 soas to output the input signal IN12 to the winding W12. It is noted thatthe power of the signal S12 generated by the winding W12 would bechanged when the amplifier 1120 is activated by an enable signal En12.The enable signals En11 and En12 may be the power supply signals of theamplifiers 1110 and 1120, control signals of a bias circuit, systemvoltages (VDD or VCC) of the radio frequency amplifier 1110 or biasvoltages of the radio frequency amplifier 1110.

Moreover, the impedance matching of the radio frequency amplifier 1110could be adjusted by enabling/disabling the amplifiers 1110 and/or 1120.In detail, the impedance matching provided by the transformer 1010 couldbe switched between a first impedance matching and a second impedancematching based on the enable signals En1 and En2. When the amplifier1110 is enabled and the amplifier 1120 is disabled, the transformer 1010provides the first impedance matching by performing a two-stageelectromagnetic induction which comprises the electromagnetic inductionbetween the windings W1 and W2 resulted from inputting the signal IN1and the electromagnetic induction between the windings W2 and W3 whichresults in the generation of the signal S3. When the amplifier 1110 isdisabled and the amplifier 1120 is enabled, the transformer 1010provides the second impedance matching. Moreover, the amplifiers 1110and 1120 may be enabled simultaneously, such that the impedance matchingprovided by the transformer 1010 is a third impedance matching.Accordingly, the impedance matching provided by the transformer 1010 isswitched among the first impedance matching, the second impedancematching and the third impedance matching. In an embodiment thetransformer ratios of the windings W11, W12 and W13 is 1:2:4, the loadimpedance of the load circuit 1130 is 50Ω. Therefore, the firstimpedance matching is equal to 50/4=12.5Ω, the second impedance matchingis equal to 50/2=25Ω, and a typical value (i.e. equivalent value) ofthird impedance matching is equal to

$\frac{\left( {25 \times 12.5} \right)}{\left( {25 + 12.5} \right)} = {8.3\mspace{11mu}{\Omega.}}$Thus, the second impedance matching is greater than the first impedancematching, and the third impedance matching is less than the firstimpedance matching and the second impedance matching. In anotherembodiment of the present invention, the second impedance matching isless than the first impedance matching, and the third impedance matchingis less than the first impedance matching and the second impedancematching.

Moreover, the operation of inputting the input signal IN11 to thewinding W11 is performed according to the enable signal En11, and theoperation of inputting the input signal IN12 to the winding W12 isperformed according to the enable signal En12. The transformer 1010 mayprovide the first impedance matching by inputting the input signal IN11to the winding W11, such that the load impedance of the output signalSOUT matches the input signal IN11. Moreover, the transformer 1010 mayprovide the second impedance matching by inputting the input signal IN12to the winding W12, such that the load impedance of the output signalSOUT matches the input signal IN12. Therefore, by inputting the inputsignal IN11 or IN12, the impedance matching provided by the transformer1010 would be switched between the first impedance matching and thesecond impedance matching. Wherein, the transformer 1010 provides thefirst impedance matching when the input signal IN11 is inputted and theinput signal IN12 is not inputted. The transformer 1010 provides thesecond impedance matching when the input signal IN11 is not inputted andthe input signal IN12 is inputted. Moreover, when both of the inputsignals IN11 and IN12 are inputted, the transformer 1010 provides thethird impedance matching.

Moreover, the output power of the RF amplifier 1100 could be adjustedaccording to the enable signals En11 and En12. In other words, if theoutput power of the RF amplifier 1100 is equal to PW11 when theamplifier 1110 is enabled and the amplifier 1120 is disabled, and if theoutput power of the RF amplifier 1100 is equal to PW12 when theamplifier 1110 is disabled and the amplifier 1120 is enabled, then theoutput power of the RF amplifier 1100 is substantially equal to(PW11+PW12) when both of the amplifiers 1110 and 1120 are enabled andthe energy losses are ignored. Therefore, the output power of the RFamplifier 1100 could be switched to 0, PW11, PW12 or (PW11+PW12)according to the enable signals En11 and En12. Accordingly, variousdemands for the output power of the RF amplifier 1100 would besatisfied.

In an embodiment of the present invention, it is supposed that thewinding W11 has an equivalent inductance I11, the winding W2 has anequivalent inductance I12 and the winding W3 has an equivalentinductance I13. The equivalent inductances I11, I12 and I13 aresequentially increasing or decreasing, and such relationships among theequivalent inductances I11, I12 and I13 may be determined according tothe practical demands of the application of the circuit (e.g. gain,efficiency, power, SNR, etc.). In other words, relationships among theequivalent inductances I11, I12 and I13 may be I11>I12>I13 orI11<I12<I13. The equivalent inductances I11, I12 and I13 would bedetermined by adjusting the turns or widths of the windings W11, W12 andW13. Take adjusting the turns of the windings W11, W12 and W13 forexample, if I11>I12>I13, a number of turns of the winding W11 is greaterthan a number of turns of the winding W12, and the number of turns ofthe winding W12 is greater than a number of turns of the winding W13.Take adjusting the widths of the windings W11, W12 and W13 for example,if I11>I12>I13, the width of the winding W11 is less than the width ofthe winding W12, and the width of the winding W12 is less than the widthof the winding W13.

In an embodiment of the present invention, I11<I12<I13 and the outputpower of the amplifier 1120 is less than the output power of theamplifier 1110. For example, if the ratios of I11:I12:I13 are 1:2:4,then the transformer ratios of the windings W1, W2 and W3 would be also1:2:4. Therefore, the second impedance matching would be greater thanthe first impedance matching, and the typical value of the thirdimpedance matching would be less than the first impedance matching andthe second impedance matching. Accordingly, a greater output power has aless impedance matching. In another embodiment of the present invention,I11>I12>I13 and the output power of the amplifier 1120 is greater thanthe output power of the amplifier 1110. Since the transformer 1010outputs the signal S13 by performing the two-stage electromagneticinduction by the windings W1, W2 and W3, as compared to a prior arttransformer which performs single-stage electromagnetic induction, thetransformer 1010 of the present invention has a smaller constant qualityfactor circle (constant Q circle), the transformer 1010 and the RFamplifier 1100 have a greater bandwidth and a less insertion loss.Moreover, the transformer 1010 would have a smaller compact area in acondition that the transformer ratios are the same.

In an embodiment of the present invention, the RF amplifier 1100 is usedas a transmitter in a radio frequency (RF) device, and the input signalsIN11 and IN12 are two different RF signals. According to the enablesignals En11 and En12, the output power of the transmitter of the RFdevice could be switched among various output powers and the impedancematching of the RF amplifier 1100 could be adjusted simultaneously.

Moreover, if the amplifier 1120 is a differential amplifier, a capacitorC may be added and coupled between two output ends T13 and T14 of theamplifier 1120. In the condition that the impedance matchings to whichthe RF amplifier 1100 could be switched are fixed, the requiredequivalent inductances of the windings W11, W12 and W13 could be reducedby connecting a plurality of the capacitors C with the windings W11, W12and W13 in parallel.

In a preferred embodiment of the present invention, if few flux lossresulted from routing the windings is ignored, the windings W11 and W12are substantially completely magnetically coupled, the windings W12 andW13 are substantially completely magnetically coupled, and the windingW13 is substantially completely magnetically isolated from the windingW11. In an embodiment of the present invention, the distance between thewindings W11 and W13 is not too great, such that the windings W11 andW13 would be substantially completely magnetically coupled if thewinding W12 is not provided to supply magnetic isolation between thewindings W11 and W13. Moreover, the plane on which the windings W11, W12and W13 are positioned is parallel with a reference plane or coincideswith the reference plane, and geometry centers of the three windingsW11, W12 and W13 projected on the reference plane substantially coincidewith each other. A plurality of embodiments of the present inventionwould be set forth in the below description. Please refer to FIG. 11.FIG. 11 is a layout diagram of a transformer 1010 according to anembodiment of the present invention. In the embodiment, the referenceplane is XY plane formed by X axis and Y axis, and a section B11 of thewinding W11, a plurality of sections B12 of the winding W12 and aplurality of sections B13 of the winding W13 are positioned within eacharea 2101 or 2102 on XY plane. The section B11, the sections B12 and thesections B13 are parallel within the area 2101 or 2102. Moreover, thesections B12 are positioned adjacent to two sides of the section B11 andadjacent inner sides of the sections B13. Due to the foresaid positingof the windings W11, W12 and W13, the windings W11 and W12 aresubstantially completely magnetically coupled, the windings W12 and W13are substantially completely magnetically coupled, and the winding W13is substantially completely magnetically isolated from the winding W11by the winding W12. Moreover, the windings W11, W12 and W13 from aninner ring 240 and an outer ring 250. The inner ring 240 is formedwithin a plurality of areas 2101, and the outer ring is formed within aplurality of areas 2102. The geometry centers of the windings W11, W12and W13 (i.e. the centers of the areas surrounded by the windings W11,W12 and W13) are a point O on the XY plane or almost coincide with eachother. Moreover, the sections of the windings W11, W12 and W13 withinthe areas 2103 and 2104 are formed on different planes. The sections B12of the winding W12 within the areas 2103 and 2104 stretch over thesections B11 of the winding W11, and the sections B13 of the winding W13within the areas 2103 and 2104 stretch over the sections B12 of thewinding W12. The two sections B12 of the winding W12 within the area2103 are interlaced and not contact to each other so as to connect thesections B12 within the inner ring 240 and the outer ring 250. The twosections B11 of the winding W11 within the area 2104 are interlaced andnot contact to each other so as to connect the sections B11 within theinner ring 240 and the outer ring 250. The two sections B13 of thewinding W13 within the area 2104 are interlaced and not contact to eachother so as to connect the sections B13 within the inner ring 240 andthe outer ring 250. In an embodiment of the present invention, thesections B12 of the winding W12 within the area 2013 completely overlapthe entire area 2103 so as to isolate the sections B11 within the area2103 from the sections B13 within the area 2103. In an embodiment of thepresent invention, the windings W11, W12 and W13 are respectively formedby the sections B11, B12 and B13 within a single area 2101 or 2102 asshown in FIG. 12. The geometry center of the section B11, the geometrycenter of the sections B12 and the geometry center of the sections B13are a point O′ on the XY plane or almost coincide with each other. FIG.12 is an enlarged view of the windings W11, W12 and W13 located withinan area 2101 or 2102 shown in FIG. 11. FIG. 12 is similar with FIG. 4.FIG. 12 could be obtained by replacing the sections B1, B2 and B5 ofFIG. 4 by sections B11, B12 and B13 respectively.

In an embodiment of the present invention, an exploded diagram ofanother transformer 1010 could be referred the descriptions of FIG. 6and obtained by replacing the winding W1, the winding W2, the first partL1, the ends P1 to P4 and P9 to P10 of FIG. 6 by the winding W11, thewinding W12, the winding W13, and the ends P101 to P106 respectively.

In an embodiment of the present invention, diagrams of anothertransformer 1010 could be referred the descriptions of FIGS. 7-9 andobtained by replacing the winding W1, the winding W2, the first part L1,the ends P1 to P4 and P9 to P10 of FIGS. 7-9 by the winding W11, thewinding W12, the winding W13, and the ends P101 to P106 respectively.

In summary, the embodiments of the present invention providetransformers, and each of the transformers has a third windingmagnetically isolated from a first winding by a second winding.Moreover, the transformer outputs a third signal by performing atwo-stage electromagnetic induction by the first winding, the secondwinding and the third winding. As compared to a prior art transformerwhich performs single-stage electromagnetic induction, the transformerof the present invention has a smaller constant quality factor circle(constant Q circle). Accordingly, as compared to the prior arttransformer, the transformer and the RF amplifier of the presentinvention have a greater bandwidth and a less insertion loss. In acondition that the transformer according to the present invention hasthe same transformer ratios as the prior, the transformer of the presentinvention has a smaller compact area. Moreover, the RF amplifier of thepresent invention would obtain optimum impedance matchings for differentoutput powers.

Those skilled in the art will readily observe that numerousmodifications and alterations of the device and method may be made whileretaining the teachings of the invention. Accordingly, the abovedisclosure should be construed as limited only by the metes and boundsof the appended claims.

What is claimed is:
 1. A transformer, comprising: a first winding; asecond winding; a third winding; a fourth winding; and a fifth windingcomprising a first part and a second part serially connected to thefirst part, the first part being magnetically coupled to the secondwinding and magnetically isolated from the first winding, and the secondpart being magnetically coupled to the fourth winding and magneticallyisolated from the third winding; wherein the second winding ispositioned between the first winding and the first part, the firstwinding is positioned adjacent to the second winding, and the secondwinding is positioned adjacent to the first part; wherein the fourthwinding is positioned between the third winding and the second part, thethird winding is positioned adjacent to the fourth winding, and thefourth winding is positioned adjacent to the second part; wherein thetransformer is coupled to a first amplifier, a second amplifier, a thirdamplifier, and a fourth amplifier; wherein an output end of a firstamplifier is coupled to an end of the first winding, and the firstamplifier operates according to a first enable signal so as to output afirst input signal to the first winding; wherein an output end of asecond amplifier is coupled to an end of the second winding, and thesecond amplifier operates according to a second enable signal so as tooutput a second input signal to the second winding; wherein an outputend of a third amplifier is coupled to an end of the third winding, andthe third amplifier operates according to a third enable signal so as tooutput a third input signal to the third winding; and wherein an outputend of a fourth amplifier is coupled to an end of the fourth winding,and the fourth amplifier operates according to a fourth enable signal soas to output a fourth input signal to the fourth winding; wherein afirst equivalent inductance of the first winding is greater than asecond equivalent inductance of the second winding, the secondequivalent inductance of the second winding is greater than a fifthequivalent inductance of the first part of the fifth winding, a thirdequivalent inductance of the third winding is greater than a fourthequivalent inductance of the fourth winding, the fourth equivalentinductance of the fourth winding is greater than a sixth equivalentinductance of the second part of the fifth winding, an output power ofthe second amplifier is greater than an output power of the firstamplifier, and an output power of the fourth amplifier is greater thanan output power of the third amplifier.
 2. The transformer of claim 1,wherein the first part of the fifth winding is magnetically isolatedfrom the first winding by the second winding, and the second part of thefifth winding is magnetically isolated from the third winding by thefourth winding.
 3. The transformer of claim 1, wherein sections of thefirst winding, sections of the second winding and sections of the firstpart are positioned on a same plane, and the sections of the first partare magnetically isolated from the sections of the first winding by thesections of the second winding; wherein sections of the third winding,sections of the fourth winding and sections of the second part arepositioned on a same plane, and the sections of the second part aremagnetically isolated from the sections of the third winding by thesections of the fourth winding.
 4. The transformer of claim 3, whereinthe plane comprises at least a first area, and a first section of thefirst winding, a plurality of second sections of the second winding anda plurality of third sections of the first part are positioned withinthe first area of the same plane, the first section, the second sectionsand the third sections are parallel, and the second sections arepositioned adjacent to two sides of the first section and adjacent innersides of the third sections.
 5. The transformer of claim 3, wherein theplane comprises at least a first area, and plurality of first sectionsof the first winding, a plurality of second sections of the secondwinding and a third section of the first part are positioned within thefirst area of the same plane, the first sections, the second sectionsand the third section are parallel, and the second sections arepositioned adjacent to two sides of the third section and adjacent innersides of the first sections.
 6. The transformer of claim 3, wherein theplane comprises at least a second area, and a fourth section of thethird winding, a plurality of fifth sections of the fourth winding and aplurality of sixth sections of the second part are positioned within thesecond area of the same plane, the fourth section, the fifth sectionsand the sixth sections are parallel, and the fifth sections arepositioned adjacent to two sides of the fourth section and adjacentinner sides of the sixth sections.
 7. The transformer of claim 3,wherein the plane comprises at least a second area, and a plurality offourth sections of the third winding, a plurality of fifth sections ofthe fourth winding and a sixth section of the second part are positionedwithin the second area of the same plane, the fourth sections, the fifthsections and the sixth section are parallel, and the fifth sections arepositioned adjacent to two sides of the sixth section and adjacent innersides of the fourth sections.
 8. The transformer of claim 1, wherein thefirst winding, the second winding and the first part of the fifthwinding are positioned on three different parallel planes, the thirdwinding, the fourth winding and the second part of the fifth winding arepositioned on three different parallel planes, the first part of thefifth winding is magnetically isolated from the first winding by atleast a first conductor, and the second part of the fifth winding ismagnetically isolated from the third winding by at least a secondconductor.
 9. The transformer of claim 8, wherein the second winding andthe at least a first conductor are positioned on a same plane, and thefourth winding and the at least a second conductor are positioned on asame plane.
 10. The transformer of claim 9, wherein the at least a firstconductor and/or the at least a second conductor is grounded.
 11. Thetransformer of claim 9, wherein the at least a first conductor comprisestwo first conductors respectively positioned adjacent to an outer sideand an inner side of the second winding, and the at least a secondconductor comprises two second conductors respectively positionedadjacent to an outer side and an inner side of the fourth winding.
 12. Atransformer, comprising: a first winding; a second winding; a thirdwinding; a fourth winding; and a fifth winding comprising a first partand a second part serially connected to the first part, the first partbeing magnetically coupled to the second winding and magneticallyisolated from the first winding, and the second part being magneticallycoupled to the fourth winding and magnetically isolated from the thirdwinding; wherein the second winding is positioned between the firstwinding and the first part, the first winding is positioned adjacent tothe second winding, and the second winding is positioned adjacent to thefirst part; wherein the fourth winding is positioned between the thirdwinding and the second part, the third winding is positioned adjacent tothe fourth winding, and the fourth winding is positioned adjacent to thesecond part; wherein the transformer is coupled to a first amplifier, asecond amplifier, a third amplifier, and a fourth amplifier; wherein anoutput end of a first amplifier is coupled to an end of the firstwinding, and the first amplifier operates according to a first enablesignal so as to output a first input signal to the first winding;wherein an output end of a second amplifier is coupled to an end of thesecond winding, and the second amplifier operates according to a secondenable signal so as to output a second input signal to the secondwinding; wherein an output end of a third amplifier is coupled to an endof the third winding, and the third amplifier operates according to athird enable signal so as to output a third input signal to the thirdwinding; and wherein an output end of a fourth amplifier is coupled toan end of the fourth winding, and the fourth amplifier operatesaccording to a fourth enable signal so as to output a fourth inputsignal to the fourth winding; wherein a first equivalent inductance ofthe first winding is less than a second equivalent inductance of thesecond winding, the second equivalent inductance of the second windingis less than a fifth equivalent inductance of the first part of thefifth winding, a third equivalent inductance of the third winding isless than a fourth equivalent inductance of the fourth winding, thefourth equivalent inductance of the fourth winding is less than a sixthequivalent inductance of the second part of the fifth winding, an outputpower of the second amplifier is less than an output power of the firstamplifier, and an output power of the fourth amplifier is less than anoutput power of the third amplifier.